1. Field of Invention
This invention relates to devices for automatically supplying liquid samples to analytical instruments and, more particularly, to such devices wherein an intake tube is lowered into a sample source and at particular points in an operating cycle the intake tube is lowered into vessles containing neutal or calibration solutions.
2. Description of the Prior Art
In conventional prior art apparatus, the samples were contained in sample vessels, which were mounted in a circular array on a turntable, that was movable in a stepwise manner. During the movement of the turntable, the sample vessels one after the other would come into the area of a stationary intake tube, which was lowered therein to withdraw a liquid sample, that was thence supplied to the analytical instrument in an appropriate manner. It will be appreciated, that for quantitative analysis, it is necessary to calibrate the analytical instrument. For this purpose, a neutral solution, i.e. a solution that does not contain the substance being tested for, is supplied to the analytical instrument, in order to determine the zero line. In addition, a calibration solution, having a known concentration, is supplied to the analytical instrument and, by setting the signal evaluation circuit, the analytical instrument can then be adjusted so that an indication of zero is obtained with the neutral solution and an indication of the known value of the calibration solution is obtained with the calibration solution. It can then be assumed that the concentration of an unknown sample will be indicated correctly. However, in many analytical instruments, the calibration is dependent on the test condition, which may vary in the course of a series of measurements. Therefore, it is necessary to make another calibration after a certain number of analyses. For this purpose, prior art devices had vessels containing a neutral or null solution and vessels containing a calibration solution arranged in predetermined places in the circular array of sample vessels on the turntable. When these vessels came into the area of the intake tube, the analytical instrument would automatically be switched to its calibration mode. See, for example, German patent No. 2,111,609.
In prior art devices of the type described above, the vessels containing the neutral or calibration solutions were placed on the sample vessel turntable and the switching-over of the analytical instrument to its calibration mode was effected by the movement of the turntable, As a result, the capacity of the turntable was substantially reduced, because spaces which could otherwise be used for sample solutions were used by the neutral and calibration vessels. Moreover, the prior art devices were not flexible, as the calibration vessels could only be located in particular predetermined places on the turntable. Thus, it was impossible to vary the number of sample analyses between calibrations, depending on the respective requirements. In addition, it was difficult with prior art devices to use a plurality of different calibration solutions in the case of non-linear sensitivity characteristics. Moreover, such prior art devices involved the risk of faulty operation due to misplacement of the calibration vessels on the turbtable. It is further noted that in such prior art devices the samples, of necessity, had to be contained in vessels on a turntable.